In the field of orthopaedics, it is well known to utilize various compression hip screw devices. Typically, a compression hip screw includes a lag screw with a tube or hollow barrel disposed over the lag screw and a compression screw threadably coupled to the lag screw. The barrel and the lag screw extend into the bone with the lag screw extending across the fracture. A bone plate typically extends from the barrel for attachment to the bone with bone screws. The compression screw permits application of a compressive force between the plate and the lag screw.
It is known to provide compression hip screws which include an intergaging key between the lag screw and the barrel to prevent rotation therebetween. Such keyed devices are shown in U.S. Pat. No. 2,702,543 to Pugh et al. and U.S. Pat. No. 4,095,591 to Graham, Jr. et al. Other such devices are provided without any keyed portion between the lag screw and barrel which allows rotation therebetween and thus does not require the alignment necessary with keyed devices. An example of such a device is the KEY-FREE.TM. Compression Hip Screw which was sold by Zimmer, Inc. of Warsaw, Ind.
Various compression hip screw assemblies provide for a separately insertable locking member of various configurations as disclosed by the following: U.S. Pat. Nos. 4,432,358 and 4,657,001 to Fixel; U.S. Pat. No. 4,530,355 to Griggs; U.S. Pat. No. 4,612,920 to Lower; and U.S. Pat. No. 4,759,352 to Lozier. In Griggs and Lower and Lozier, the separately insertable locking member may optionally be used if a keyed device is desired, or selectively not inserted if a keyless device is desired. Whether or not a keyed or keyless system is utilized typically depends upon the preference of the surgeon. While these devices provide the option for a keyed or keyless device, the separately insertable locking member or key can be inconvenient to line up and insert during a surgical procedure if a keyed device is desired by the surgeon.